1. Field of the Invention
The present invention relates to a network communication apparatus, and in particular to a network communication apparatus to be installed aboard a watercraft or the like.
2. Description of the Related Art
In the automobile field or the like, in response to a trend where devices are modularized and are rendered intelligent and the number of harnesses is reduced, device control based on serial communication including Controller Area Network (CAN) communication is being introduced rapidly.
In the automobile field, devices to be connected to and controlled through a communication line are fixed from a development stage, and the device connection will never be altered at least after shipment as a product.
FIG. 5 is a block diagram showing a conventional example of a CAN system installed aboard an automobile. In FIG. 5, reference numeral 111 denotes an accelerator position Electronic Control Unit (ECU) that is an ECU for measuring an accelerator opening degree and is given a node ID “ID#1”. Reference numeral 112 represents a throttle actuator ECU that is an ECU for driving an electronically controlled throttle and is given a node ID “ID#2”. Reference numeral 113 indicates an engine ECU that is an ECU for controlling an engine and is given a node ID “ID#3”. Reference numeral 114 denotes a shift lever ECU that is an ECU for detecting a position of shift lever and is given a node ID “ID#5”. Reference numeral 115 represents an AT ECU that is an ECU for controlling an automatic transmission and is given a node ID “ID#4”. Reference numeral 108 indicates a communication line A that constitutes a network based on a CAN technique. Reference numeral 116 denotes a network A constructed by all the aforementioned construction elements.
The node IDs “ID#1” to “ID#5” set in FIG. 5 are fixed at a design stage and, once an automobile or the like provided with this network is sold, there will never be made an alteration to the device connection such as the detaching of the shift lever ECU 114.
Accordingly, it is possible to determine, at the design stage, a procedure to be executed in serial communication including communication based on the CAN system installed aboard an automobile, with the procedure being executed to identify each device (node), to specify the function thereof, and to judge whether or not the network is established as a system.
In the watercraft field, however, in contrast to the automobile field described above, an engine manufacturer only supplies an engine, for instance. Therefore, a boat builder performs assembling of a watercraft. Also, there is a case where the watercraft is provided with a plurality of engines or a plurality of maneuvering seats, for instance. Therefore, even if the same engine is used, specifications of completed watercrafts vary depending on users. As a result, it is difficult for the engine manufacturer to control the specifications of the completed watercrafts.
As described above, it is difficult for the engine manufacturer to control the specifications of the completed watercrafts. However, each apparatus possesses an independent control means and a fault warning means, which allows a network to be established as a system without any problem.
FIG. 9 schematically shows a conventional watercraft system. In FIG. 9, reference numeral 121 denotes a right remote controller; 122, a left remote controller; 123, an indicator panel; 124, a right throttle wire; 125, a left throttle wire; 126, a right engine rpm signal line; 127, a left engine rpm signal line; 128, a right engine warning signal line; 129, a left engine warning signal line; 130, a right engine; 131, a left engine; 132, a key switch (key SW); and 133, a key switch signal line for establishing connections among the key switch 132, the indicator panel 123, the right engine 130, and the left engine 131.
In FIG. 9, the right remote controller 121 is connected to the right engine 130 through the right throttle wire 124 and controls the throttle opening degree of the right engine 130 by means of wire tension. The left remote controller 122 is connected to the left engine 131 through the left throttle wire 125 and controls the throttle opening degree of the left engine 131 by means of wire tension. The indicator panel 123 is an apparatus for displaying an rpm of the engine and an engine warning state. To do so, the indicator panel 123 obtains the rpm of the right engine 130 through the right engine rpm signal line 126, obtains the rpm of the left engine 131 through the left engine rpm signal line 127, obtains a warning state of the right engine 130 through the right engine warning signal line 128, obtains a warning state of the left engine 131 through the left engine warning signal line 129, and displays these obtained information. The key switch 132 is an apparatus for starting the engines, and when a key is inserted into a key switch ECU (not shown) and is turned, the key switch signal line 133 is energized, thereby starting the indicator panel 123, the right engine 130, and the left engine 131.
In FIG. 9, one engine rpm signal line and one warning signal line are provided for each engine, so that a system is simply established in a manner such that a single engine arrangement is obtained if only one engine is connected, and a twin engine arrangement is obtained if two engines are connected.
In a network based on the CAN technique, a BUS-shaped network is constructed by H/W (hardware) in compliance with CAN specifications, and communication is performed through arbitration with reference to priorities specified by CAN-IDs.
In a conventional example, when various apparatuses are networked, control information, fault information, and the like that are independently managed by each of these apparatuses will be dealt with in a consolidated manner. In the watercraft field, assembling is performed by the boat builder as described above, so that whether all apparatuses are to be networked or only some thereof are networked and conventional apparatuses are to be used as the remaining apparatuses depends on a judgment made by the boat builder or a user. Consequently, although a specifying means each apparatus connected to the network is required, respective nodes are equally dealt with under the CAN specifications and are not given names (that is, identifiers such as node IDs).
FIG. 8 shows an example in which the same watercraft system as in FIG. 9 is constructed using a BUS-shaped network in compliance only with the CAN specifications. In FIG. 8, a right remote controller 141, a left remote controller 142, an indicator panel 143, a right engine 150, and a left engine 151 are connected to one another through a single-channel CAN-bus 144. A key switch (key SW) 152 is an apparatus for starting the engines, and when a key is inserted into a key switch ECU (not shown) and is turned, a key switch signal line 153 is energized, thereby starting the indicator panel 143, the right remote controller 141, the left remote controller 142, the right engine 150, and the left engine 151.
In the case of an automobile system or the like in which IDs are fixed in advance, such a network is established as a system. In the case of a watercraft system, however, it is not undefined whether a single engine arrangement or a twin engine arrangement is to be used, and therefore, both of these arrangement have a chance to be used by a boat builder at the time of assembling. Therefore, when the left engine 151 does not exist at the time of start, for instance, it is impossible to discriminate whether the single engine arrangement is used for the system from the beginning or wire breaking occurs in a part of the network and therefore no data reaches from the left engine 151. That is, it is impossible to discriminate whether or not the network is established as a system. It is also impossible to specify correspondences between the right and left engines and the right and left remote controllers. Further, even if an engine rpm or warning information is transmitted from the right or left engine, it is impossible to display the information on the indicator panel 143 while discriminating whether this information is a value from the right engine or the left engine.
Also, in the watercraft field, survivability is highly demanded. However, if a BUS-shaped network is used like in the aforementioned conventional example, there is a high possibility that when a fault occurs only in a part of the network, the watercraft loses its maneuvering function. As a result, a minimum return-to-port means needs to be provided.
FIG. 3 is a block diagram of a watercraft system using a BUS-shaped network in compliance only with the CAN specifications. In this drawing, reference numeral 105 denotes a remote control ECU (node D) that functions as a user interface through which a target throttle opening degree and a shift position (forward/reverse) are specified. Reference numeral 106 represents a steering ECU (node E) that functions as a user interface through which a target steering (rudder) angle is specified. Reference numeral 102 indicates a management node key switch ECU (node A) that is an ECU for detecting a key switch state. Reference numeral 103 denotes a shift and throttle actuator ECU (node B) that is an ECU for controlling a shift and throttle actuator in accordance with the target throttle opening degree and the target shift position. Reference numeral 104 represents a steering actuator ECU (node C) that is an ECU for controlling a rudder actuator in accordance with the target steering angle. Reference numeral 168 indicates hardware for a single-channel CAN copy network. Reference numeral 101 denotes a communication line A (CAN1ch), with reference symbol 101 are presenting a location at which wire breaking occurs in the communication line A 101. Reference numeral 107 indicates a network B constructed by all of these construction elements.
In FIG. 3, when wire breaking occurs at the location 101a, information from the remote control ECU 105 and the steering ECU 106 does not reach the key switch ECU 102, the shift and throttle actuator ECU 103, and the steering actuator ECU 104. As a result, there occurs a situation where maneuvering of the watercraft becomes totally impossible.
In order to obtain a high fault resistance, there may be conceived a construction where the CAN-bus 101 is duplexed, for instance. In many cases, however, a CAN function is embedded in the CPU of each node, which leads to a possibility that even if the CPU possesses a bus function for a double-channel CAN network, a fault occurs in the CPU or a short-circuit fault occurs in either of the CAN buses. As a result, the CAN function on the other side may be harmed and therefore the whole of the network may fall into an error state.
The network shown in FIG. 3 is composed of a single-channel CAN network, and if a short-circuit fault or the like occurs in any of the hardware 168 for a single-channel CAN designated by the triangular marks in FIG. 3, the communication line A 101 loses all of its functions.